In recent years, the realization of a size reduction in liquid crystal display devices has led to widespread use of liquid crystal display devices, for example, in portable telephones (cellular phones) and PDAs. In the small-size liquid crystal display devices, in addition to power saving, an increase in luminance and an increase in contrast are an important task to be attained. To attain the above task, reflection-type or semitransmission-type liquid crystal display devices for power saving and optical elements for improving the luminance and contrast for these liquid crystal display devices have been developed.
A liquid crystal display device, in which a reflection film, formed of a metal film of aluminum or the like-having openings through which light can be transmitted, functions as a light semitransmission film, has been proposed as one form of the semitransmission-type liquid crystal display device. In this semitransmission-type liquid crystal display device, a liquid crystal layer, which causes a quarter-wave phase shift in a non-voltage-applied state, is held between a pair of glass substrates. A semitransmission reflection layer and a transparent electrode formed of a transparent electrically conductive film of indium tin oxide (hereinafter abbreviated to “ITO”) or the like are stacked on the inner face of the lower (backlight side) glass substrate, and an aligning film is provided so as to cover this transparent electrode. On the other hand, a transparent electrode formed of a transparent electrically conductive film of ITO or the like is formed on the inner face of the upper (display face side) glass substrate, and an aligning film is provided so as to cover this transparent electrode. A quarter-wave plate and a polarizing plate are disposed in that order from the substrate side on the outer face side of the upper glass substrate. On the other hand, a quarter-wave plate and a polarizing plate are provided in that order from the substrate side on the outer face side of the lower glass substrate. The quarter-wave plate is an optical element that, in a certain wavelength region, can convert linearly polarized light to substantially circularly polarized light.
In the semitransmission-type liquid crystal display device having the above construction, in light from the backlight, the light part reflected from the reflection layer undergoes a change in the polarization axis by the quarter-wave plate disposed on the lower side (backlight side) of the reflection layer and is disadvantageously absorbed in the polarizing plate provided on the lower side (backlight side) of the quarter-wave plate. Consequently, light cannot be recycled, and satisfactory luminance cannot be provided. The light from the backlight and transmitted through openings in the reflection layer and through the quarter-wave plate is circularly polarized light. The half of the transmitted light is disadvantageously absorbed in the polarizing plate provided on the upper substrate. This poses a problem that satisfactory lightness and contrast cannot be provided.
To overcome the above problems, there have been proposed a semitransmission-type liquid crystal display device in which the cell gap between the transmission part and the reflection part has been regulated and the quarter-wave plate has been provided only on the reflection layer part. In this liquid crystal display device, a pair of retardation layers of the backlight side and the display side can be omitted, and, thus, the display device can realize a high level of luminance and a reduction in thickness of the display device.
Regarding the above semitransmission-type liquid crystal display device, for example, Japanese Patent Laid-Open No. 4494/2004 discloses a semitransmission-type liquid crystal display device comprising a reflection layer which has been patterned in any desired form. A retardation layer (quarter-wave plate) is provided only in the reflection display region. In this liquid crystal display device, light from the backlight and reflected from the reflection layer is not absorbed in the retardation layer, and, thus, light can be recycled. In this technique, good lightness and contrast are realized by regulating the cell gap in the transmission display region and the reflection display region so that, in the non-voltage-applied state, the phase shift of the liquid crystal layer in the transmission display region is half wavelength and the phase shift of the liquid crystal layer in the reflection display region is quarter wavelength.
Doornkamp et al. proposes a semitransmission-type liquid crystal display device having excellent lightness and contrast by regulating the cell gap in the transmission display region and the reflection display region so that, in the non-voltage-applied state, the phase shift of the liquid crystal layer in the transmission display region is half wavelength, and the phase shift of the liquid crystal layer in the reflection display region is quarter-wavelength, and providing a retardation plate (quarter-wave plate) only in the color filter part in the reflection display region (C. Doornkamp et al., SDI 2004 Digest, 670 (2004)).
Thus, in order to provide a retardation layer only in the reflection display region, the retardation layer should also be patterned in a form corresponding to reflection layer patterned in any desired form.
In the method described in Japanese Patent Laid-Open No. 4494/2004, however, photolithography is used for patterning of the retardation layer, and, thus, the production process is complicated. This has made it difficult to produce a liquid crystal display device in a cost-effective manner. That is, the photolithographic process comprises providing a photosensitive resin layer on the retardation layer, patterning the photosensitive resin layer in any desired form, etching the retardation layer using the photosensitive resin layer as a mask, and allowing the retardation layer to locally remain unremoved to form a retardation layer which has been patterned in any desired form. Accordingly, a plurality of steps has been necessary for patterning of the retardation layer.
Further, according to the proposal of Doornkamp et al., a part of the resin is cured by light irradiation through a photomask for patterning of the retardation layer, and the resin in the uncured part is cured by light irradiation. Therefore, the exposure should be carried out twice, and the development of a simpler method has been desired.